Indole-diterpene gene cluster from Aspergillus flavus. (49/348)

Aflatrem is a potent tremorgenic mycotoxin produced by the soil fungus Aspergillus flavus and is a member of a large structurally diverse group of secondary metabolites known as indole-diterpenes. By using degenerate primers for conserved domains of fungal geranylgeranyl diphosphate synthases, we cloned two genes, atmG and ggsA (an apparent pseudogene), from A. flavus. Adjacent to atmG are two other genes, atmC and atmM. These three genes have 64 to 70% amino acid sequence similarity and conserved synteny with a cluster of orthologous genes, paxG, paxC, and paxM, from Penicillium paxilli which are required for indole-diterpene biosynthesis. atmG, atmC, and atmM are coordinately expressed, with transcript levels dramatically increasing at the onset of aflatrem biosynthesis. A genomic copy of atmM can complement a paxM deletion mutant of P. paxilli, demonstrating that atmM is a functional homolog of paxM. Thus, atmG, atmC, and atmM are necessary, but not sufficient, for aflatrem biosynthesis by A. flavus. This provides the first genetic evidence for the biosynthetic pathway of aflatrem in A. flavus.  (+info)

Prevalence of Aspergillus species in clinical samples isolated in an Indian tertiary care hospital. (50/348)

CONTEXT (BACKGROUND): In recent times, it has become important to determine the prevalence of different Aspergillus species in clinical samples in view of difference in antifungal susceptibility noted in some species. AIMS: To determine the species prevalence of Aspergillus isolates in various clinical samples received in the Mycology Laboratory at our institute. METHOD: Over a period of 4-years, a total of 18,731 samples were processed, and species identification carried out by standard microbiological methods. RESULTS: Four hundred and fifty six samples (2.43%) were culture positive for Aspergillus species. A.flavus (46.93%) was the most common isolate, followed by A.fumigatus (37.72%) and A.niger (15.35%). It was observed that A.fumigatus was the predominant species isolated from blood and respiratory specimens, A.flavus was predominantly isolated from nasal polyps whereas A.niger predominated in nail specimens. Culture positivity was highest in the age group 12-65 years and in males. Sixty-nine patients (15.13%) were admitted to the intensive care unit. CONCLUSIONS: The study highlights the diverse manifestations caused by Aspergillus species in human beings and also throws light on the different species prevalent locally. The knowledge would prove useful in selecting empirical antifungal therapy and formulating prophylactic and pre-emptive strategies.  (+info)

Growth promotion and yield enhancement of peanut (Arachis hypogaea L.) by application of plant growth-promoting rhizobacteria. (51/348)

Although plant growth-promoting rhizobacteria (PGPR) have been reported to influence plant growth, yield and nutrient uptake by an array of mechanisms, the specific traits by which PGPR promote plant growth, yield and nutrient uptake were limited to the expression of one or more of the traits expressed at a given environment of plant-microbe interaction. We selected nine different isolates of PGPR from a pool of 233 rhizobacterial isolates obtained from the peanut rhizosphere on the basis of ACC-deaminase activity. The nine isolates were selected, initially, on the basis of germinating seed bioassay in which the root length of the seedling was enhanced significantly over the untreated control. All the nine isolates were identified as Pseudomonas spp. Four of these isolates, viz. PGPR1, PGPR2, PGPR4 and PGPR7 (all fluorescent pseudomonads), were the best in producing siderophore and indole acetic acid (IAA). In addition to IAA and siderophore-producing attributes, Pseudomonas fluorescens PGPR1 also possessed the characters like tri-calcium phosphate solubilization, ammonification and inhibited Aspergillus niger and A. flavus in vitro. P. fluorescens PGPR2 differed from PGPR1 in the sense that it did not show ammonification. In addition to the traits exhibited by PGPR1, PGPR4 showed strong in vitro inhibition to Sclerotium rolfsii. The performances of these selected plant growth-promoting rhizobacterial isolates were repeatedly evaluated for 3 years in pot and field trials. Seed inoculation of these three isolates, viz. PGPR1, PGPR2 and PGPR4, resulted in a significantly higher pod yield than the control, in pots, during rainy and post-rainy seasons. The contents of nitrogen and phosphorus in soil, shoot and kernel were also enhanced significantly in treatments inoculated with these rhizobacterial isolates in pots during both the seasons. In the field trials, however, there was wide variation in the performance of the PGPR isolates in enhancing the growth and yield of peanut in different years. Plant growth-promoting fluorescent pseudomonad isolates, viz. PGPR1, PGPR2 and PGPR4, significantly enhanced pod yield (23-26%, 24-28% and 18-24%, respectively), haulm yield and nodule dry weight over the control in 3 years. Other attributes like root length, pod number, 100-kernel mass, shelling out-turn and nodule number were also enhanced. Seed bacterization with plant growth-promoting P. fluorescens isolates, viz. PGPR1, PGPR2 and PGPR4, suppressed the soil-borne fungal diseases like collar rot of peanut caused by A. niger and PGPR4 also suppressed stem rot caused by S. rolfsii. Studies on the growth patterns of PGPR isolates utilizing the seed leachate as the sole source of C and N indicated that PGPR4 isolate was the best in utilizing the seed leachate of peanut, cultivar JL24. Studies on the rhizosphere competence of the PGPR isolates, evaluated on the basis of spontaneous rifampicin resistance, indicated that PGPR7 was the best rhizoplane colonizer and PGPR1 was the best rhizosphere colonizer. Although the presence of growth-promoting traits in vitro does not guarantee that an isolate will be plant growth promoting in nature, results suggested that besides ACC-deaminase activity of the PGPR isolates, expression of one or more of the traits like suppression of phytopathogens, solubilization of tri-calcium phosphate, production of siderophore and/or nodulation promotion might have contributed to the enhancement of growth, yield and nutrient uptake of peanut.  (+info)

Monochrome LightCycler PCR assay for detection and quantification of five common species of Candida and Aspergillus. (52/348)

Invasive fungal pathogens, especially in immunocompromised hosts, can result in life-threatening infections. Current laboratory/radiological methods for fungal identification are time-consuming and lack sensitivity and specificity. A monochrome, multiplex, real-time PCR assay for the identification and quantification of Candida albicans, Candida krusei, Candida tropicalis, Aspergillus flavus and Aspergillus fumigatus is described here. Detection of each of these fungi was specific and demonstrated 100 % concordance with biochemical/culture identification in all 60 isolates tested. Samples from 16 febrile neutropenic patients with haematological malignancies were also analysed and the utility of the assay in clinical samples was reconfirmed without false-negative results. The sensitivity of this assay was 0.1 pg fungal genomic DNA, corresponding to three cells, for C. albicans, C. krusei, C. tropicalis and A. flavus, and 0.01 pg fungal genomic DNA, i.e. less than one cell, for A. fumigatus. The analysis allows a low-cost, simple, rapid and sensitive alternative for clinical identification and quantification of these five common fungal species.  (+info)

Nosocomial Aspergillus flavus wound infections following cardiac surgery. (53/348)

In this report we describe three cases of Aspergillus flavus sternal wound infection following cardiac surgery. All three cases occurred in a 3-month period coinciding with hospital renovation activities. The patients were successfully treated with combined surgical and medical therapy.  (+info)

A fraction from Escherichia coli with anti-Aspergillus properties. (54/348)

The products of various strains of Escherichia coli (BL21, DH5alpha, HB101 and XL Blue) were investigated for antimycotic properties using pathogenic isolates of Aspergillus. Co-culture experiments revealed that E. coli strains exhibited variable activity against Aspergillus fumigatus. The lysates prepared from DH5alpha, HB101 and XL Blue strains of E. coli showed inhibitory activity against A. fumigatus in the protein concentration range of 62.50 to 250.00 microg ml(-1). The highest activity was seen in the lysate of BL21, which inhibited the growth of A. fumigatus and Aspergillus flavus completely at a concentration of 31.25 microg protein ml(-1). The MIC of BL21 lysate against Aspergillus niger was found to be 62.50 microg ml(-1). The in vitro toxicity of BL21 lysate was evaluated using a haemolytic assay. A BL21 lysate protein concentration of 1250.00 microg ml(-1) was found to be nontoxic to human erythrocytes. The standard drug amphotericin B lysed 100 % of erythrocytes at a concentration of 37.50 microg ml(-1). SDS-PAGE showed the presence of at least 15 major proteins in the lysate of BL21. Ion-exchange chromatography resolved the BL21 lysate into five fractions and fraction III was found to be endowed with anti-Aspergillus properties. The MIC of this fraction was found to be 3.90 microg ml(-1). Further work on the purification of the active molecule and its characterization is in progress.  (+info)

MR features of cerebral aspergillosis in an immunocompetent patient: correlation with histology and elemental analysis. (55/348)

We report an unusual case of cerebral aspergillosis in a young immunocompetent patient who also had dissemination to other end organs. The patient presented with a large mass in the left cerebral hemisphere. Elemental analysis of biopsy specimens revealed elevated levels of iron, magnesium, zinc, calcium, chromium, and nickel that correlated with a peripheral rim of hypointensity on T2-weighted images.  (+info)

Discordant rise in galactomannan antigenemia in a patient with resolving Aspergillosis, renal failure, and ongoing hemodialysis. (56/348)

We describe the case of a patient with improving invasive aspergillosis and paradoxically rising serum galactomannan levels in the presence of chronic renal failure and ongoing hemodialysis. Dialysate tested negative for galactomannan, demonstrating the inability of treatments such as hemodialysis to clear Aspergillus antigen from serum. In patients with renal failure and aspergillosis, rising serum galactomannan levels may not necessarily signify progressive infection.  (+info)